The present invention relates to an electric apparatus of the contact maker-breaker kind using the same power contacts for both the make and break functions.
Such electric apparatus of the contact maker-breaker kind are well known and comprise for example:
at least one pole with separable contacts, called power contacts;
an electromagnet having a coil adapted to be fed by current pulses forming closing and opening orders generated in response to the actuation of a manual control member, and a mobile armature to which a control mechanism is coupled, this control mechanism being adapted for closing and opening the contacts as a function of the order transmitted to the coil;
an automatic tripping device associated with said pole and causing the contacts to open following the detection of a short circuit;
a quenching device associated with each cut-off chamber.
In such apparatus which combine the "contact maker" function and the "contact breaker" function, a current limitation function is integrated solely with the "contact breaker" function, which function is fulfilled for example by a magnetic striker on each pole, for protecting the contacts at the time of a short circuit.
Now, since such apparatus use the same contacts for the "contact maker" function and the "contact breaker" function, it is also desirable to protect the contacts when they are controlled by the electromagnet so as to prevent in particular any possible appearance of the known phenomenon of bounce during closing of the contacts.
The object of the invention is to provide an electric apparatus of the contact maker-breaker kind using the same power contacts for the contact maker and contact breaker functions, which provides excellent protection, in a simple way, of the contacts not only during closing or opening by manual control, but also during automatic tripping on a fault.
For this, the basic idea of the contact maker-breaker according to the invention resides in the fact that the power contacts are associated in series with a superconducting element which is controlled thermally and structured so as to have a very high resistance following its controlled transition from the superconducting state to the normal state in response to a closing or opening order or following its intrinsic transition from the superconducting state to the normal state in response to a fault current, so that the contacts close and open on the same so-called leak current, of very low value.
The result of this leak current is advantageously that no electric arc is then likely to occur between the contacts, which makes it possible henceforth to omit any arc quenching structure, contrary to the prior art.